As disclosed in U.S. Pat. No. 4,146,688 (Schwindt et al.), it is known that phenylenediamines which bear a single ar-hydrocarbylthio substituent and optionally also a single ar-alkyl substituent can be used as chain extenders for polyurethane resins. However, the use of these known chain extenders can create toxicity and/or discoloration problems.
U.S. Pat. No. 4,595,742 (Nalepa et al.) discloses phenylenediamine chain extenders which bear at least two ar-alkylthio substituents and preferably also an ar-alkyl substituent. These chain extenders lack the disadvantages of the chain extenders of Schwindt et al. and are ordinarily quite suitable for the preparation of urethane and urea polymers having desirable properties. However, in some applications, e.g., in the preparation of room temperature coatings and in the preparation of polymers by RIM processes, the gel times provided by the chain extenders are sometimes slower than is desired.
U.S. Pat. Nos. 4,594,453 (Ranken et al.), 4,670,598 (Davis-I), and 4,751,330 (Davis-II) teach that phenylenediamines bearing at least one ar-hydrocarbylthio substituent can be prepared by reacting a phenylenediamine, optionally bearing an ar-alkyl substituent, with a hydrocarbyldisulfide in the presence of a Lewis acid catalyst.